Intruder,
Flightaware has the following for NW188:
Scheduled Dep: 2:35PM PDT
Scheduled Arr: 7:47PM CDT (3 hours 12 minutes)
Seven Day Running Average for this flight
Actual Departure 2:38PM PDT
Actual Arrival 7:50PM CDT
Oct 21 Flight
Actual Departure 3:00PM PDT
Actual Arrival: 8:54PM CDT
Quite sure that ATC would not have had them fly a loopy return if fuel on-board was becoming critical.